A retrospective study on the prevalence of pre-XDR and XDR Mycobacterium tuberculosis in the South Coastal Region of Andhra Pradesh, India

Background: The emergence of pre-extensively drug-resistant tuberculosis (pre-XDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) represents a major public health challenge in India. This study assessed the prevalence and genetic profiles of drug-resistant Mycobacterium tuberculosis (MTB) isolates in the south coastal region of Andhra Pradesh. Materials and Methods: A retrospective analysis was carried out on 5759 smear-positive sputum samples collected in 2024. The GenoType MTBDRplus and MTBDRsl Ver 2.0 line probe assays were used to detect resistance to first-line drugs—rifampicin (RIF) and isoniazid (INH) and second-line drugs (SLDs)—fluoroquinolones (FQs) and second-line injectable drugs (SLIDs). Demographic and molecular data were analyzed to determine resistance patterns and mutation profiles. Results: Of 5759 samples, 5699 yielded valid results. Among these, a total of 5114 (89.73%) isolates were fully susceptible, while 585 (10.26%) exhibited drug resistance. INH mono-resistance was most common (N=450;7.89%), followed by RIF mono-resistance (N=41;0.72%). Multidrug-resistant TB (MDR-TB) was identified in 94 cases (1.65%), of these 9 (9.6%) were classified as pre-XDR-TB (MDR-TB with additional FQ resistance), and 2 (2.1%) as XDR-TB (MDR-TB with resistance to both FQs and at least one SLID) and rest 83 (88.30%) were susceptible to SLDs. The predominant mutations were katG S315T1 and rpoB S531L for INH and RIF resistance. All pre-XDR isolates exhibited gyrA mutations conferring FQ resistance, while one XDR isolate harbored rrs A1401G and the other showed eis promoter mutations accounting for SLID resistance. Conclusions: Although the study highlights a predominance of drug-susceptible TB in South Coastal Andhra Pradesh, it also reveals a growing concern regarding the increasing prevalence of MDR-TB, pre-XDR-TB, and XDR-TB.